I have started a 4L started for a pilsner im going to brew this saturday. Its (2) 2L started and I started it on Thursday in a 1.045 solution with a second generation pilsner yeast cake. I have them both on stir plates and at 45 degrees fareignheit and 6 hours into it I have massive amounts of CO2 being produced. So much that when I stop the stir bar it looks like I just poured a hefeweizen there is so much CO2 running up the side of the flask. My question is, is this ok? Ive done quite a handful of started but this is however my first with a second generation yeast and I have never seen this before. From my understanding, CO2 is produced after the reproduction phase which quite frankly is all were after with a starter right..reproduction. So with all of this CO2 being produced does this mean that there is little to no reproduction of yeast cells?

The whole cake? You wouldn't need a starter if your using the cake, unless my mind is completely f'd, which it is a lot of times. Someone else will chime in, though, and correct me if I'm ignorantly wrong...however, the yeast cake from a batch, even second generation (or did you mean secondary yeast cake?), has a whole @@@ton of yeast cells in it. My first thought is, you took hundreds of billions, multiple hundreds of billions of yeast cells and threw them in a starter, that is going to go off like nuts. Absolutely crazy and fast.

EDIT: Probably un-needed as well. If you are making a higher gravity beer this go around, you could just top it on top without any starter, or rinse the yeast and suspend it and pour it directly into primary.

Well this is what I got after washing the remnants after coming out of the secondary. It might have only been about one inch up the side of a small mason jar max. Still just a lot of yeast though. Im just wondering about the CO2 though. I want to replicate cells and if CO2 is being produced this means that the cells appear to have gone straight to consumption of the sugars instead of replicating does it not?

I apologize as well, if you were washing, you didn't end up taking ALL of the yeast cake? Still though, I'd say the reaction is due to a crap ton of them. Once you hit your max m/ml pitch rate in a starter, reproduction as I understand it (I AM NOT A MICROBIOLOGIST), you will not have any effective cell reproduction, I have no idea how many billion yeast cells you threw in. From my calculations if you threw more than say 520 billion yeast cells into a 2 L starter, your new cells created will be virtually non-existant. You would be pitching at a rate of over 250 million cells per millileter.

Until someone says I am right, you should take that with a grain of salt. You still should have healthy yeast though, I just would try either a much bigger container (maybe a gallon?)

Thanks everyone. I decided to throw so much in because it was about one month from the time I washed the yeast (which was after about four weeks in a secondary) to the time I started the starter and I figured my viability would be nill. Guess I was a little wrong on that haha. Thanks everyone.